Normally, when running a pipe or rod string into or out of a borehole, a clamping device is utilized to suspend the string in the hole while another joint or section is threaded onto the top of the string or removed from the string.
In the past, these clamping devices have consisted of toothed clamping collars which are levered against the casing by external levers and linkages. An example of this type device is shown in U.S. Pat. Nos. 1,552,062 and 1,654,866. Other types of clamps utilize conical toothed inserts located in a tapered cylinder which are wedged against the tubing or rod. An example of this device is shown in U.S. Pat. No. 1,017,305.
The deficiencies of these devices include their complexity, their inability to hold properly under all conditions, and the difficulty of installing from the middle of a long string section when the ends of the string are not readily accessible.
This invention solves the above problem by providing an inner toothed, generally cylindrical, unitary gripping member located concentrically and pivotably in a flanged container or abutment housing and encircling the pipe or rod to be clamped and suspended. The invention utilizes the pipe strings own weight to establish a rotational moment in the gripping member which forces the gripping member toward gripping engagement with the tubing or rod string.
This invention also provides a gripping member particularly advantageous for use in a well packer for gripping engagement with the packer mandrel to prevent unsetting of the packer. The gripping means used in the prior art devices utilize multiple wedge inserts having internal teeth therein. These wedge inserts are driven inward against the mandrel by externally applied forces acting on a cammed driver sleeve which slides up on the sloping faces of the wedge inserts thereby driving them inward. The actuating force on this type of gripping means must be constantly maintained or else slipping of the mandrel and unsetting of the packer will occur. Any additional forces on the packer tending to unset it, such as formation pressure surges, require an accompanying increase in force to be applied externally to the wedge inserts to prevent unsetting of the packer by the pressure surge.
This invention overcomes this disadvantage by providing an unitary gripping sleeve with dual axis bore passage therethrough; with a portion of said bore passage having internal gripping teeth therein. The sleeve locks against the mandrel by rotating against it and is arranged such that surge forces and compressive forces in the packer elements serve to rotate the sleeve into even tighter engagement with the mandrel thereby preventing unsetting of the packer.